Sizing Grounding Electrode Conductors

[mtnelectrical]

When using ground rods as a grounding electrodes, how do you size the conductor to use?

 

[JES2727]

Table 250.66

 

[Dennis Alwon]

T. 250.66 is for electrodes however, you never need more than a #6 to the rod. I believe with #4 wire as service conductors you could actually use #8 but never larger than #6

 

[mtnelectrical]

so I does no matter the size of the service. Even a 400 amps , only requires a #6 wire, right?

 

[mtnelectrical]

and when are 3/4" ground rods required?

 

[MasterTheNEC]

and when are 3/4" ground rods required?

When the designer specifies them, if they so choose or when it is a "pipe" electrode. See below:

"(5) Rod and Pipe Electrodes. Rod and pipe electrodes shall not be less than 2.44 m (8 ft) in length and shall consist of the following materials.

(a) Grounding electrodes of pipe or conduit shall not be smaller than metric designator 21 (trade size 3∕4) and, where of steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.

(b) Rod-type grounding electrodes of stainless steel and copper or zinc coated steel shall be at least 15.87 mm (5∕8 in.) in diameter, unless listed."

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[Dale001289]

so I does no matter the size of the service. Even a 400 amps , only requires a #6 wire, right?

Look at 250.66(A).

 

[Dennis Alwon]

so I does no matter the size of the service. Even a 400 amps , only requires a #6 wire, right?

Correct-- 3000 amp service only needs a #6 to the rod

 

[tom baker]

Table 250.66

Actually its section 250.66, as the section gives exemptions to the sizes in Table 250.66, take a look at 250.66(A) for your answer

 

[tom baker]

Larger dia electrodes are often used where rods are driven deeper than 10 ft.

 

[MasterTheNEC]

Actually its section 250.66, as the section gives exemptions to the sizes in Table 250.66, take a look at 250.66(A) for your answer

Well lets not actually call them exceptions fella... *grin*...we on that panel like to call them permitted applications inlieu of the general rule.

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[infinity]

Well lets not actually call them exceptions fella... *grin*...we on that panel like to call them permitted applications inlieu of the general rule.

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

For the record he called them exemptions.

 

[MasterTheNEC]

For the record he called them exemptions.

Snap...never thought of them that way. My appologies

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[MasterTheNEC]

Actually its section 250.66, as the section gives exemptions to the sizes in Table 250.66, take a look at 250.66(A) for your answer

My bad Tom....sorry fella

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[MasterTheNEC]

Note to self - Exemptions - permitted applications inlieu of the general rule.

I am going to submit that definition...lol...but i am probably the only sucker to read that poorly...lol...

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17